Crystalline aluminum carbide thin film, semiconductor substrate having the aluminum carbide thin film formed thereon and method of fabricating the same

ABSTRACT

Embodiments of the invention provide a crystalline aluminum carbide thin film, a semiconductor substrate having the crystalline aluminum carbide thin film formed thereon, and a method of fabricating the same. Further, the method of fabricating the AlC thin film includes supplying a carbon containing gas and an aluminum containing gas to a furnace, to growing AlC crystals on a substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/091,581, filed on Apr. 21, 2011, which claims priority from and thebenefit of Japanese Patent Application No. JP2011-016085, filed on Jan.28, 2011, which is hereby incorporated by reference for all purposes asif fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a crystallinealuminum carbide thin film, a semiconductor substrate having acrystalline aluminum carbide thin film formed thereon, and a method offabricating the same.

2. Discussion of the Background

A light emitting diode (LED) including a gallium nitride (GaN) basedsemiconductor may be used for various applications, such as signaldevices, backlight units for liquid crystal panels, and the like. SinceAlGaInN-based LEDs have a wavelength band of 260˜290 nm or 360˜600 nm,an AlGaN-based active layer may be included to produce a shorterwavelength band (300˜340 nm). As such, Al_(x)Ga_(1-x)N-basedsemiconductor materials have been continuously developed. At awavelength of 280 nm, it is possible to obtain a light extractionefficiency of 10% or more.

However, since AlGaN is liable to be split and has higher dislocationdensity, an AlGaN material used in a wavelength band from 300 nm to 360nm has not yet been developed. Current reports say that LEDs exhibit alight extraction efficiency of at most 8%, in a wavelength band of300˜350 nm.

Generally, elements located at an upper part of the periodic table emitlight at shorter wavelengths. Although BN or C have the shortestwavelengths, these components are not suited for general light emittingmaterials, since the growth of these materials requires hightemperatures of 2500° C. or more. AlN may be used instead of thesematerials. Namely, investigations have been made to develop a materialthat emits light at a short wavelength (λ=210 nm) using AlN. However,AlGaN has a low light extraction efficiency, as described above.

Meanwhile, aluminum carbide Al₄C₃ (hereinafter, “AlC”) is an importantcompound in aluminum technology, due to its high electric resistance andhigh thermal conductivity at room temperature. Since AlCN, which is analuminum compound similar to AlC, can be used in various applications,such as microelectronics, photonic technology, and the like, due to itswide band gap, high chemical stability, and high hardness, AlC is alsoanticipated to have the same capabilities as AlCN. AlC is a III-IVgroup-based material and is generally known as a nano-processingmaterial.

In order to use AlC for a semiconductor substrate, particularly, forLEDs, it is necessary to provide a thin film exhibiting excellentcrystallinity. However, crystalline thin films formed using AlC has notyet been developed. Currently, only a non-crystalline thin film of AlCis reported by L. Yate et al., Surface and Coatings Technology, 203,1904 (2009).

SUMMARY OF THE INVENTION

Exemplary embodiments of the invention provide a crystalline aluminumcarbide thin film, a semiconductor substrate having the crystallinealuminum carbide thin film formed thereon, and a method of fabricatingthe same.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the invention provides a crystalline aluminumcarbide (AlC) thin film. The AlC thin film may emit light at awavelength in the range of 310 nm to 413 nm in cathode luminescence (CL)measurement. The AlC thin film may have a band gap from 3.4 eV to 4.3 eVin a transmittance measurement. The AlC thin film may be formed on asapphire substrate or a silicon carbide substrate. The AlC thin film maybe formed on a c-plane of the sapphire substrate.

An exemplary embodiment of the invention provides a semiconductorsubstrate having a crystalline AlC thin film.

An exemplary embodiment of the invention provides a method offabricating an AlC thin film. The method includes supplying acarbon-containing gas and an aluminum-containing gas to form an AlC thinfilm, by growing AlC crystals on a substrate.

An exemplary embodiment of the invention provides a method offabricating a semiconductor substrate having an AlC thin film formedthereon. The method includes supplying a carbon-containing gas and analuminum containing gas to form an AlC thin film, by growing a AlCcrystals on a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a view of a semiconductor substrate, in accordance with anexemplary embodiment of the invention.

FIG. 2 is a graph depicting conditions for fabricating an AlC thin filmon the semiconductor substrate, in accordance with an exemplaryembodiment of the invention.

FIG. 3( a) shows a relationship between a growth temperature and agrowth rate of an AlC thin film, in accordance with an exemplaryembodiment of the invention.

FIG. 3( b) shows a relationship between a flow rate of TMA and a growthrate of the AlC thin film.

FIG. 3( c) shows a relationship between a IV/III ratio and the growthrate of the AlC thin film.

FIG. 4( a) is a scanning electron microscope (SEM) image of an AlC thinfilm formed at 700° C.

FIG. 4( b) is a (SEM) image of an AlC thin film formed at 1150° C.

FIG. 4( c) is a scanning electron microscope (SEM) image of an AlC thinfilm formed at 1200° C.

FIG. 5( a) is an SEM image of a side section of a semiconductorsubstrate having an AlC film formed at 1150° C.

FIG. 5( b) is an SEM image of a side section of a semiconductorsubstrate having an AlC film formed at 1200° C.

FIG. 6 is a graph of an XRD measurement of the semiconductor substrate.

FIG. 7( a) is an SEM image of a side section of the semiconductorsubstrate.

FIG. 7( b) shows an energy dispersive X-ray spectrometer (EDX) resultfor aluminum detection.

FIG. 7( c) shows an EXD result for carbon detection.

FIG. 7( d) shows an EXD result for oxygen detection.

FIG. 8( a) shows a CL measurement of an AlC thin film formed at 700° C.

FIG. 8( b) shows a CL measurement of an AlC thin film formed at 1200° C.

FIG. 9 is a graph depicting a result of transmittance measurement forthe semiconductor substrate having the AlC thin film.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein. Rather, these exemplary embodiments are provided so thatthis disclosure is thorough, and will fully convey the scope of theinvention to those skilled in the art. In the drawings, the sizes andrelative sizes of layers and regions may be exaggerated for clarity.Like elements will be denoted by like reference numerals and repeateddescriptions thereof will be omitted herein.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent.

The inventors of the invention investigated materials, fabricationconditions, and the like to obtain a crystalline aluminum carbide thinfilm (hereinafter, referred to as an “AlC thin film”) and finallydeveloped a crystalline AlC thin film on a c-plane of the sapphiresubstrate.

An AlC thin film, according to an exemplary embodiment of the presentdisclosure, may be evaluated using a scanning electron microscope (SEM),X-ray diffraction (XRD), an energy dispersive x-ray spectrometer (EDX),cathode luminescence (CL), and/or a transmittance measurement. SinceAl₄C₃ generally has a yellow color, when the AlC thin film is formed ona substrate formed of a different material than the AlC thin film, AlCthin film can be observed with the naked eye or an optical microscope,in that the substrate appears to have a yellow color. Further, it can beseen through SEM observation that crystals are grown on the substrate.Through an SEM image of a side section of the substrate, the AlC thinfilm is shown to be formed on the substrate.

The AlC thin film has a peak near 35° in 20-w mode of XRD, which iscaused by Al₄C₃ crystals. Further, when the AlC thin film is formed on asubstrate having a different crystal structure from the Al₄C₃ crystals,peaks caused by the crystals of the substrate are also detected. Forexample, when the AlC thin film is formed on a c-plane of a sapphiresubstrate, peaks near 38° and 42° are detected, which are caused by thesapphire substrate.

An EDX image shows the presence of aluminum and carbon in the AlC thinfilm. In the EDX image showing the presence of aluminum and carbon,since the AlC thin film has crystallinity, aluminum and carbon aredetected in a dispersed state. The aluminum and carbon may be uniformlydispersed in the AlC thin film.

In a CL measurement, the AlC thin film emits light in a wavelength rangeof from 310 nm to 413 nm, which is caused by the Al₄C₃ crystals. The AlCthin film has a peak near 340 nm and exhibits light extraction in awavelength band of 300-350 nm, when used in an LED.

In a transmittance measurement, the AlC thin film has a band gap of from3.4 eV to 4.3 eV. Further, the AlC thin film has a direct transition inthe region of the band gap, that is, in a luminescence energy region.Here, the direct transition refers to a state in which the square of thetransmittance ratio is proportional to energy, in a plot of valuesobtained by dividing the transmittance ratio of the Al₄C₃/substrate bythe transmittance ratio of the substrate, with respect to the energy.Further, the AlC thin film may be adjusted to have an indirect band gap,by adjusting a fabrication temperature thereof.

As described above, although only a non-crystalline AlC thin film hasbeen reported in the art, the present crystalline AlC thin film may beapplied to a crystalline semiconductor layer, which demonstrates thecharacteristics described above. Further, when used in an LED, the AlCthin film exhibits light extraction in the wavelength band of 300-350nm.

FIG. 1 is a view of a semiconductor substrate 100, in accordance with anexemplary embodiment of the invention. The semiconductor substrate 100includes an AlC thin film 10 formed on an upper surface of a substrate20. Here, the substrate 20 may be any type of substrate that can be usedfor AlC crystal growth in the field of semiconductors, particularly, inthe field of LEDs. For example, the substrate 20 may be a sapphiresubstrate or a silicon carbide substrate. When the sapphire substrate isused as the substrate 20, the AlC thin film 10 may be formed on ac-plane of the sapphire substrate 20.

The semiconductor substrate 100 may be evaluated using a scanningelectron microscope (SEM), X-ray diffraction (XRD), energy dispersivex-ray spectroscopy (EDX), cathode luminescence (CL), and transmittancemeasurements.

When observed with the naked eye or an optical microscope, the AlC thinfilm 10 formed on the substrate 20 can be observed to impart a yellowcolor to the substrate. Further, using a SEM, it can be seen thatcrystals are grown on the substrate 20. Through an SEM image of a sidesection of the substrate, the AlC thin film 10 is shown to be formed onthe substrate 20.

The AlC thin film 10 has a peak near 35° in 20-w mode of XRD, which iscaused by Al₄C₃ crystals. Further, peaks caused by the crystal of thesubstrate 20 are detected, in addition to the peaks caused by the Al₄C₃crystals. For example, when the AlC thin film 10 is formed on a c-planeof the sapphire substrate 20, peaks near 38° and 42° are detected, whichare caused by the sapphire substrate 20.

An EDX image shows the presence of aluminum and carbon in thesemiconductor substrate 100. In the EDX image showing the presence ofaluminum and carbon, since the AlC thin film 10 is crystalline, aluminumand carbon are detected in a dispersed state. In this embodiment,aluminum and carbon may be uniformly dispersed in the AlC thin film 10.Further, when a sapphire substrate is used as the substrate 20, aluminumis also detected in the sapphire substrate, whereas carbon is detectedin the AlC thin film 10.

In a CL measurement, the semiconductor substrate 100 emits light in thewavelength range of from 310 nm to 413 nm, as a result of the Al₄C₃crystals. The semiconductor substrate 100 has a peak near 340 nm andexhibits light extraction in a wavelength band of 300-350 nm, when usedin an LED.

In transmittance measurement, the semiconductor substrate 100 has a bandgap of from 3.4 eV to 4.3 eV. Further, the semiconductor substrate 100has a direct transition in the region of the band gap, that is, in aluminescence energy region. Further, the semiconductor substrate 100 maybe adjusted to have an indirect band gap, by controlling the fabricationtemperature thereof.

As described above, although an AlC thin film only for a non-crystallinethin film has been reported in the art, the semiconductor substrate 100may allow a crystalline AlC thin film to be formed. Accordingly, thesemiconductor substrate 100 demonstrates the characteristics describedabove. Further, when used in an LED, the semiconductor substrate 100exhibits light extraction in the wavelength band of 300-350 nm.

Metal organic vapor deposition (MOCVD) may be used to fabricate thecrystalline AlC thin 10 film and the semiconductor substrate 100. Inthis embodiment, the crystalline AlC thin film 10 is grown on an uppersurface of the substrate 20.

Raw materials for the AlC thin film 10 include a carbon-containing gasand an aluminum-containing gas. The carbon-containing gas may be methane(CH₄) and the aluminum-containing gas may be tri-methyl aluminum((CH₃)₃Al; hereinafter “TMA”). Further, hydrogen (H₂) may be used as acarrier gas. The respective raw materials may be commercial materialsused in the field of semiconductors, particularly, in the field of LEDs.

The TMA may be may be supplied at flow rates of from 33 μmol/min to 66μmol/min, and the methane may be supplied at flow rates of 13 mmol/minto 27 mmol/min, to grow the AlC crystals. Further, the AlC crystals aregrown at a temperature of 700° C. or more, or at a temperature of 1100°C. or more. Although time for growing the AlC crystals depends on theflow rate of raw materials and/or the thickness of the AlC thin film 10,the time for growing the AlC crystals may be in the range of, forexample, 60-120 minutes. The substrate 20 may be annealed, by supplyinghydrogen gas before growing the AlC crystals. Annealing may be performedat 1150° C. for 10 minutes, for example, when the flow rate of hydrogengas is 10 slm.

By the method described above, it is possible to form a crystalline AlCthin film on a semiconductor substrate. Accordingly, the semiconductorsubstrate demonstrates the characteristics described above. Further,when used in an LED, the semiconductor substrate exhibits lightextraction in the wavelength band of 300-350 nm.

FIG. 2 is a graph depicting conditions for fabricating the AlC thin film10 formed on the semiconductor substrate 100, in accordance with anexemplary embodiment of the invention. In FIG. 2, “Car(III)” indicatesthe flow rate of hydrogen supplied as the carrier gas of TMA, “Car(IV)”indicates the flow rate of hydrogen supplied as the carrier gas of CH₄,“Sub” indicates the flow rate of hydrogen for re-dilution of Car(III)and Car(IV), and “Counter” indicates the flow rate of nitrogen towardsan upper side of a furnace that faces the substrate 100.

FIG. 3( a) shows a relationship between the growth temperature and thegrowth rate of the AlC thin film 10. Although the AlC thin film 10 couldbe grown at a temperature of 700° C., the growth rate was slow at thistemperature. A meaningful growth rate could be measured beginning at atemperature of 1100° C. Further, a furnace used for this example wasoperated at a temperature of 1200° C.

FIGS. 4( a), 4(b), and 4(c) are SEM images of AlC thin films formed at700° C., 1150° C., and 1200° C., respectively. Each of the figures isobtained by observing the semiconductor substrate 100 including the AlCthin film 10, from an upper side of the substrate 100. In this example,a SM6499 (Nippon Electronic Corporation) was used as the SEM. At agrowth temperature of 1150° C. or more, AlC crystals were observed.

FIGS. 5( a) and 5(b) are SEM images of side sections of semiconductorsubstrates 100 having AlC thin films formed at 1150° C. and 1200° C.,respectively. At 1150° C. and 1200° C., it was observed that AlC thinfilms 10 were formed on the upper surface of the substrates 20.

FIG. 3( b) shows the relationship between the flow rates of TMA and thegrowth rates of AlC thin films. In this example, the growth temperaturewas set to 1150° C. and the flow rate of methane was set to 13.4mmol/min. The flow rate of TMA was set to 5.1 μmol/min, 6.6 μmol/min, 33μmol/min, and 66 μmol/min. As the flow rate of TMA increased, the growthrate of the AlC thin film increased.

FIG. 3( c) shows a relationship between the IV/III ratio and the growthrate of the AlC thin films. In this example, the growth temperature wasset to 1150° C. The IV/III ratio was set to 203, 406, 812, 4032, and5261. At a IV/III ratio of 406, the highest growth rate was achieved.

FIG. 6 shows XRD measurement results. In this example, an X'pert MRD(Philips Co., Ltd.) was used as the XRD apparatus. The peaks caused bysapphire used for the substrate were observed near 38° and 42°. For theAlC thin films formed at 1100° C. and 1150° C., a peak caused by theAl₄C₃ crystals was detected near 35°, in addition to the peaks caused bysapphire. The AlC thin film formed even at a growth temperature of 700°C. had low growth efficiency. As a result, when the thin film was grownfor 60 minutes in this example, the Al₄C₃ crystal peak was not detected.

Next, the semiconductor substrate 100 having the AlC thin film 10 formedthereon was examined by EDX. In this example, a Link ISIS (Oxford Co.,Ltd.) was used as the EDX. FIG. 7( a) is a SEM image of a side sectionof the semiconductor substrate 100, FIG. 7( b) shows a result ofaluminum detection, FIG. 7( c) shows a result of carbon detection, andFIG. 7( d) shows a result of oxygen detection. Aluminum was detected inboth the AlC thin film 10 and the sapphire substrate 20. Carbon wasdetected in the AlC thin film 10, and oxygen was detected in thesapphire substrate 20. From these results, it can be seen that the AlCthin film 10 is formed on the upper surface of the sapphire substrate20.

Next, a CL measurement was performed with respect to the semiconductorsubstrate 100 having the AlC thin film 10 formed thereon. In thisexample, a MONO CL2 (Oxford Co., Ltd.) was used as the CL testingapparatus. FIG. 8( a) shows a result of CL measurement for the AlC thinfilm 10 formed at 700° C., and FIG. 8( b) shows a result of CLmeasurement for the AlC thin film 10 formed at 1200° C. In the AlC thinfilm 10 formed at 1200° C., light emission was detected in thewavelength range of 310 nm to 413 nm, typically near a wavelength of 340nm, and the half width at half maximum was 50 nm. On the other hand, inCL measurement of the AlC thin film 10 formed at 700° C., a wide peakincluding a wavelength longer than 340 nm was detected. From theseresults, it can be assumed that the AlC thin film 10 formed at 1200° C.had good film quality.

Last, transmittance measurement was performed with respect to thesemiconductor substrate 100 having the AlC thin film 10 formed thereon.FIG. 9 is a graph depicting a result of the transmittance measurementfor the semiconductor substrate 100 having the AlC thin film 10 formedat 1200° C. In the graph of FIG. 9, the band gap of the AlC thin film 10was typically about 3.4 eV and exhibited a direct transition. In otherconditions, the AlC thin film 10 had a band gap of 3.4 eV to 4.3 eV.

As such, the exemplary embodiments of the invention provide acrystalline aluminum carbide thin film, a semiconductor substrate havingthe crystalline aluminum carbide thin film formed thereon, and a methodof fabricating the same.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of fabricating a crystalline AlC thinfilm, comprising: supplying a carbon-containing gas and analuminum-containing gas into a furnace, to grow the AlC thin film on asubstrate.
 2. The method of claim 1, wherein the AlC thin film is grownby metal organic chemical vapor deposition.
 3. The method of claim 1,wherein the substrate is a sapphire substrate or a silicon carbidesubstrate.
 4. The method of claim 3, wherein the AlC thin film is formedon a c-plane of the sapphire substrate.
 5. The method of claim 1,wherein the carbon containing gas is methane and the aluminum containinggas is tri-methyl aluminum.
 6. The method of claim 5, wherein: thetri-methyl aluminum is supplied at a flow rate of from 33 μmol/min to 66μmol/min; and the methane is supplied at a flow rate of from 13 mmol/minto 27 mmol/min.
 7. The method of claim 6, wherein the AlC thin film isgrown at a temperature of at least 700° C.
 8. The method of claim 6,wherein the AlC thin film is grown at a temperature of at least 1100° C.9. A method of fabricating a semiconductor substrate having acyrstalline AlC thin film formed thereon, comprising: supplying a carboncontaining gas and an aluminum containing gas to a furnace, grow the AlCthin film on a substrate.
 10. The method of claim 9, wherein the AlCthin film is grown by metalorganic chemical vapor deposition.
 11. Themethod of claim 9, wherein the substrate is a sapphire substrate or asilicon carbide substrate.
 12. The method of claim 9, wherein: thesubstrate is a sapphire substrate; and the AlC thin film is formed on ac-plane of the sapphire substrate.
 13. The method of claim 9, whereinthe carbon containing gas is methane and the aluminum containing gas istri-methyl aluminum.
 14. The method of claim 13, wherein: the tri-methylaluminum is supplied at a flow rate of 33 μmol/min to 66 μmol/min; andthe methane is supplied at a flow rate of 13 mmol/min to 27 mmol/min.15. The method of claim 14, wherein the AlC thin film is grown at atemperature of at least 700° C.
 16. The method of claim 14, wherein theAlC thin film is grown at a temperature of at least 1100° C.